(abridged) We introduce our survey of galaxy groups at 0.85<z<1, as an extension of the Group Environment and Evolution Collaboration (GEEC). Here we present the first results, based on Gemini GMOS-S nod-and-shuffle spectroscopy of seven galaxy groups selected from spectroscopically confirmed, extended XMM detections in COSMOS. In total we have ...

(abridged) We introduce our survey of galaxy groups at 0.85<z<1, as an extension of the Group Environment and Evolution Collaboration (GEEC). Here we present the first results, based on Gemini GMOS-S nod-and-shuffle spectroscopy of seven galaxy groups selected from spectroscopically confirmed, extended XMM detections in COSMOS. In total we have over 100 confirmed group members, and four of the groups have >15 members. The dynamical mass estimates are in good agreement with the masses estimated from the X-ray luminosity, with most of the groups having 13<log(Mdyn/Msun)<14. Our spectroscopic sample is statistically complete for all galaxies with Mstar>1E10.1 Msun, and for blue galaxies we sample masses as low as Mstar=1E8.8 Msun. Like lower-redshift groups, these systems are dominated by red galaxies, at all stellar masses Mstar>1E10.1 Msun. Few group galaxies inhabit the "blue cloud" that dominates the surrounding field; instead, we find a large and possibly distinct population of galaxies with intermediate colours. The "green valley" that exists at low redshift is instead well-populated in these groups, containing ~30 per cent of galaxies. These do not appear to be exceptionally dusty galaxies, and about half show prominent Balmer-absorption lines. Furthermore, their HST morphologies appear to be intermediate between those of red-sequence and blue-cloud galaxies of the same stellar mass. We postulate that these are a transient population, migrating from the blue cloud to the red sequence, with a star formation rate that declines with an exponential timescale 0.6 Gyr< tau < 2 Gyr. Their prominence among the group galaxy population, and the marked lack of blue, star-forming galaxies, provides evidence that the group environment either directly reduces star formation in member galaxies, or at least prevents its rejuvenation during the normal cycle of galaxy evolution. ; Comment: MNRAS, in press. Minor revisions and updated references to match published version Minimize

We present deep GMOS-S spectroscopy for 11 galaxy groups at 0.8<z<1.0, for galaxies with r_{AB}<24.75. Our sample is highly complete (>66%) for eight of the eleven groups. Using an optical-NIR colour-colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue),...

We present deep GMOS-S spectroscopy for 11 galaxy groups at 0.8<z<1.0, for galaxies with r_{AB}<24.75. Our sample is highly complete (>66%) for eight of the eleven groups. Using an optical-NIR colour-colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue), and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only ~20 per cent of the field in the mass range 10^{10.3}<M_{star}/M_\odot<10^{11.0} but are the dominant component of groups. If we assume that the properties of the field are similar to those of the `pre-accreted' population, the environment quenching efficiency (\epsilon_\rho) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is ~0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent ~20 per cent of the star-forming population in both the group and field, at all stellar masses, the average sSFR of the group population is lower by a factor of ~3. The green population does not show strong H-delta absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation (\tau) must be <2 Gyr, shorter than the 3-7 Gyr required to fit data at z=0. The relatively small fraction of intermediate galaxies requires that the actual quenching process occurs quickly, with an exponential decay timescale of \tau_q<1 Gyr. ; Comment: Accepted for publication in MNRAS. 18 pages, 20 figures Minimize

We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 < z < 1.0, for galaxies with r AB < 24.75. Our sample is highly complete (>66 per cent) for eight of the 11 groups. Using an optical–near-infrared colour–colour diagram, the galaxies in the sample were separated with a dust insensitive method into...

We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 < z < 1.0, for galaxies with r AB < 24.75. Our sample is highly complete (>66 per cent) for eight of the 11 groups. Using an optical–near-infrared colour–colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue) and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only ∼20 per cent of the field in the mass range 1010.3 < M star /M ⊙ < 1011.0, but are the dominant component of groups. If we assume that the properties of the field are similar to those of the ‘pre-accreted’ population, the environment quenching efficiency (ϵ ρ ) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is ∼0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent ∼20 per cent of the star-forming population in both the group and field, at all stellar masses, the average specific star formation rate of the group population is lower by a factor of ∼3. The green population does not show strong Hδ absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation (τ) must be ≲ 2 Gyr, shorter than the 3–7 Gyr required to fit data at z = 0. The relatively small fraction of intermediate galaxies require that the actual quenching process occurs quickly, with an exponential decay time-scale of τ q ≲ 1 Gyr. Minimize

We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 < z < 1.0, for galaxies with r AB < 24.75. Our sample is highly complete (>66 per cent) for eight of the 11 groups. Using an optical–near-infrared colour–colour diagram, the galaxies in the sample were separated with a dust insensitive method into...

We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 < z < 1.0, for galaxies with r AB < 24.75. Our sample is highly complete (>66 per cent) for eight of the 11 groups. Using an optical–near-infrared colour–colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue) and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only ∼20 per cent of the field in the mass range 1010.3 < M star /M ⊙ < 1011.0, but are the dominant component of groups. If we assume that the properties of the field are similar to those of the ‘pre-accreted’ population, the environment quenching efficiency (ϵ ρ ) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is ∼0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent ∼20 per cent of the star-forming population in both the group and field, at all stellar masses, the average specific star formation rate of the group population is lower by a factor of ∼3. The green population does not show strong Hδ absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation (τ) must be ≲ 2 Gyr, shorter than the 3–7 Gyr required to fit data at z = 0. The relatively small fraction of intermediate galaxies require that the actual quenching process occurs quickly, with an exponential decay time-scale of τ q ≲ 1 Gyr. Minimize

We present a study of the relation between dark matter halo mass and the baryonic content of host galaxies, quantified via luminosity and stellar mass. Our investigation uses 154 deg2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. We employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4. We express the relationship between halo mass and baryonic observable as a power law. For the luminosity-halo mass relation we find a slope of 1.32+/-0.06 and a normalisation of 1.19+0.06-0.07x10^13 h70^-1 Msun for red galaxies, while for blue galaxies the best-fit slope is 1.09+0.20-0.13 and the normalisation is 0.18+0.04-0.05x10^13 h70^-1 Msun. Similarly, we find a best-fit slope of 1.36+0.06-0.07 and a normalisation of 1.43+0.11-0.08x10^13 h70^-1 Msun for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98+0.08-0.07 and 0.84+0.20-0.16x10^13 h70^-1 Msun. For red lenses, the fraction which are satellites tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2x10^9 h70^-2 Msun. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy-galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to over-predicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed. [abridged] ; Comment: 29 pages, 22 figures, accepted for publication in MNRAS. Abstract abridged for arXiv submission Minimize

We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg^2 of Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the ...

We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg^2 of Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the weak lensing signal around our galaxies, we employ a galaxy–galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4, split into a red and a blue sample. We express the relationship between dark matter halo mass and baryonic observable as a power law with pivot points of 10^(11)h^(−2)_(70)L_⊙ and 2×10^(11)h^(−2)_(70)M_⊙ for luminosity and stellar mass, respectively. For the luminosity–halo mass relation, we find a slope of 1.32 ± 0.06 and a normalization of 1.19^(+0.06)_(−0.07)×10^(13)h^(−1)_(70)M_⊙ for red galaxies, while for blue galaxies the best-fitting slope is 1.09^(+0.20)_(−0.13) and the normalization is 0.18^(+0.04)_(−0.05)×10^(13)h^(−1)_(70)M_⊙. Similarly, we find a best-fitting slope of 1.36^(+0.06)_(−0.07) and a normalization of 1.43^(+0.11)_(−0.08)×10^(13)h^(−1)70M_⊙ for the stellar mass–halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98^(+0.08)_(−0.07) and 0.84^(+0.20)_(−0.16)×10^(13)h^(−1)70M_⊙. All numbers convey the 68 per cent confidence limit. For red lenses, the fraction which are satellites inside a larger halo tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2×10^(9)h^(−2)70M_⊙. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy–galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to overpredicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed. Minimize

Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with the halo mass function and for understanding the physical processes that govern the heating and cooling of the intracluster medium. In this paper, we use a sample of 206 X-ray-selected galaxy groups to investigate the scaling relation between X-ra...

Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with the halo mass function and for understanding the physical processes that govern the heating and cooling of the intracluster medium. In this paper, we use a sample of 206 X-ray-selected galaxy groups to investigate the scaling relation between X-ray luminosity (L_X) and halo mass (M_(200)) where M_(200) is derived via stacked weak gravitational lensing. This work draws upon a broad array of multi-wavelength COSMOS observations including 1.64 degrees^2 of contiguous imaging with the Advanced Camera for Surveys to a limiting magnitude of I_(F814W) = 26.5 and deep XMM-Newton/Chandra imaging to a limiting flux of 1.0 × 10^(–15) erg cm6(–2) s^(–1) in the 0.5-2 keV band. The combined depth of these two data sets allows us to probe the lensing signals of X-ray-detected structures at both higher redshifts and lower masses than previously explored. Weak lensing profiles and halo masses are derived for nine sub-samples, narrowly binned in luminosity and redshift. The COSMOS data alone are well fit by a power law, M_(200) (L_X)^α, with a slope of α = 0.66 ± 0.14. These results significantly extend the dynamic range for which the halo masses of X-ray-selected structures have been measured with weak gravitational lensing. As a result, tight constraints are obtained for the slope of the M-L_X relation. The combination of our group data with previously published cluster data demonstrates that the M-L_X relation is well described by a single power law, α = 0.64 ± 0.03, over two decades in mass, M_(200) ~ 10^(13.5)-10^(15.5) h^(–1)_72 M_☉. These results are inconsistent at the 3.7σ level with the self-similar prediction of α = 0.75. We examine the redshift dependence of the M-L_X relation and find little evidence for evolution beyond the rate predicted by self-similarity from z ~ 0.25 to z ~ 0. Minimize